Question:

salam sheik
my question is are repented not to ever commit fornication again but i
still have pleasure on the memories is that am not sincere in my
repentance?

Answer:

Walaikum salam wa rahmatu Allahi wa BarakatuHu,
May Allah reward you tremendously for your question,
and I pray that Allah benefit you much with the knowledge.

Praises are to Allah, and peace be upon prophet Muhammed.

The ulema say that there are three conditions for the repentance to be
accepted:

1. Stop it.
2. Regret doing it.
3. Have a very strong resolve to never repeat it again in the future.

Once these conditions are met, Allah erases the sin from the account.
Allah also forgives sins for seeking the path to knowledge, and devoting
yourself to the ulema. Afterwards, the actions that one does afterwards
are considered new actions, and the old sin does not return to the account.

As advice, you can study the ilm in order to replace these memories of
doing something haram with the beneficial knowledge. Also you
should try your best to avoid these thoughts so that it does not lead
you to disobeying Allah. By attending the environment of ilm, it will
keep the whispers of shaitaan away. Also you can seek a way for marriage,
and raise a family devoted to the beneficial knowledge.

For masturbation, the ulema have stated that it is forbidden. Sexual postures
involving the anus are forbidden. Permanent forms of birth control are also
forbidden.

Allah forgives for being devout eager to learn the beneficial knowledge,
and removing the shawah (desires) of the nafs (soul).

And Allah knows.